This invention relates to an ultrasonic diagnosis apparatus and particularly to a so-called tissue characteristization by reflected ultrasonic waves (hereinafter referred to as "reflection type ultrasonic wave TC") which is capable of characterizing the ultrasonic wave medium to be observed, and, more concretely, a living tissue using the ultrasonic wave reflected from said ultrasonic wave medium to be observed.
Recently, attention has focused on a TC which is capable of discriminating kinds of tissues and good or bad characteristics of them rather than on the so-called B mode ultrasonic diagnosis apparatus which assists diagnosis by observing the shape of tissues within the human body.
The existing reflection type ultrasonic TC has most often used the attenuation characteristic as the parameters for discriminating characteristics of living tissues, for example, whether it is a healthy liver or a liver suffering from cirrhosis. Used in this case in the fact that when the ultrasonic sonic wave travels a distance .DELTA.z, the sound pressure is attenuated by EXP {-.alpha.(z,f).DELTA.z}, with .alpha.(z,f) considered as a constant which changes depending on place and frequency. For example, as shown in FIG. 1, in order to know the attenuation characteristic of the region 104 between the reflecting surfaces 101, 102 in the ultrasonic wave medium 103 to be observed, the ultrasonic wave is transmitted and received through an ultrasonic vibration unit 105 placed at the position where z=0, and the ultrasonic waves reflected from the reflection surfaces 101 and 102 are received. If the power spectrum of the received signal reflected from the reflecting surface 101 is considered to be A(Z.sub.1, f) and if the power spectrum of the received signal reflected from the reflecting surface 102 is A(Z.sub.2, f), and further if the characteristics of the reflecting surfaces (reflection coefficient, etc.) are assured to be the same, then the attenuation characteristic .alpha.(z, f) can be obtained from the following relations. ##EQU1##
This attenuation characteristic can also be obtained by the method already proposed without obtaining the spectrum. However, the existing method using the attenuation characteristic as the parameter involves the following problems.
Firstly, in in the case where the reflecting surfaces 101, 102 shown in FIG. 1 have different frequency characteristics, .alpha.(z,f) obtained from the equation (1) is calculated as a frequency characteristic that is different from that of the intrinsic region 104 to be observed.
Secondly, it is said that an attenuation characteristic has a dependency on frequency of about 1 dB/MHz/cm in ordinary living tissues. But an attenuation difference of only 2 dB or so is generated at the upper and lower limits of the region even when an ultrasonic wave having a bandwidth of about 1 MHz, as is used for an ordinary ultrasonic diagnosis apparatus goes and returns through a living tissue of about 1 cm of thickness. It is accordingly hidden by disturbance of the spectrum due to disturbance of the ultrasonic wave beam pattern, and it is difficult to obtain a meaningful attentuation characteristic. For practical use, it is necessary to make the tissue thick and to obtain an average of a large amount of data, thus degrading the space and time resolution.